The present application relates to motor drive circuits and the like, and more particularly to thyristor switching devices integrated with an antiparallel diode.
Note that the points discussed below may reflect the hindsight gained from the disclosed inventions, and are not necessarily admitted to be prior art.
Thyristors have long been used for motor control and other high voltage applications. A thyristor is a semiconductor device which has fully bipolar conduction, i.e. both electrons and holes conduct current in the ON-state. By contrast, a simple MOS transistor is a purely unipolar device, i.e. the current is carried entirely (or almost entirely) by electrons in an n-type device. An IGBT (integrated gate bipolar transistor) is a partly bipolar device, in which both carrier types carry current, but the electron current is typically greater than the hole current.
The big difficulty with thyristor circuits is that a thyristor will latch, i.e. once it is turned on it will stay on for as long as voltage across it is enough to cause current to flow. A class of thyristors known as MOS-controlled thyristors (MCTs) provides a thyristor which can be both turned on and turned off by a relatively small signal applied to a gate electrode. The thyristor is a completely bipolar device, and electrons and holes are both emitted from junctions near opposite faces of the semiconductor material. Further information on MOS-controlled thyristors can be found in e.g. issued U.S. Pat. No. 7,705,368 to Rodov and Akiyama, which is commonly owned with the present application.